Danfoss Refrigerant R290 Propane in Small Hermetic Systems Installation guide

Practical Application of Refrigerant

R290 Propane in Small Hermetic Systems

COMPRESSORS

Technical information

REFRIGERATION AND AIR CONDITIONING

2 CN.60.F1.02 November 2000

Refrigerant R 290, or propane, is a possible replacement for other refrigerants, which have

high impact on environment, in small hermetic systems, like factory made commercial re-

frigerators and freezers. It has zero ozone depletion potential ODP and a neglectible global

warming potential GWP. Furthermore it is a substance which is a part of petrol gases from

natural sources.

The refrigerant R 290 has been in use in refrigeration plants in the past, and is still used in

some industrial plants. In domestic heat pumps and air conditioners R 290 has been used

in Germany for some years, however, with different level of success. Because of the

availability of propane allover the world it has been discussed widely for CFC replacement.

Propane R 290 is a possible refrigerant for this application, with good energy efficiency, but

special care has to be taken to the flammability of propane.

This paper is partly similar to the R 600a paper CN.60.E .

The properties of R 290 differ from other refrigerants commonly used in small hermetic

systems, as shown in table 1. This leads to a different design of details in many cases.

Table 1: Refrigerant data comparison

tnaregirfeR092Ra431RA404R22Ra006R

emaNenaporP-2,1,1,1

-arteT

-oruolf

enahte

erutxiM

521R

a341R

a431R

-orolhC

-oroulfid

enahtem

enatubosI

alumroFC

HC-

F4/25/44FHC

ICHC(

)

erutarepmetlacitirC

C°ni

7.691015.271.69531

thgiewraluceloM

lomk/gkni

1.442016.795.681.85

tniopgnilioblamroN

C°ni

1.24-5.62-8.54-8.04-6.11-

erusserP

)etulosba(rabniC°52-ta

30.270.105.210.285.0

ytisneddiuqiL

l/gkniC°52-ta

65.073.142.163.106.0

ytisnedruopaV

tta

³m/gkniC°23+/52-

6.34.40.010.73.1

yticapaccirtemuloV

³m/JkniC°23/55/52-ta

461185643314421373

noitasiropavfoyplahtnE

gk/JkniC°52-ta

604612681322673

erusserP

)etulosba(rabniC°02+ta

4.87.50.111.90.3

1 Refrigerant

November 2000 CN.60.F1.02 3

A difference between R 290 and R 134a is found in the pressure level, which is closer to R

22 and R 404A, e.g. at -25 °C evaporation the pressure is roughly 190 % of R 134a, 81 %

of R 404A, 350% of R 600a or almost exactly that of R 22. In connection with this the

normal boiling point is close to R 22 also. Evaporators will thus have to be designed similar

as for R 22 or R 404A.

Figure 1: Vapour pressure of different refrigerants versus temperature

The pressure level and critical temperature are almost like R 22. However, the discharge

temperature is much lower. This gives the opportunity to work at higher pressure ratios,

means lower evaporating temperatures, or at higher suction gas temperatures.

1.1 Pressure

-50 -40 -30 -20 -10 0 10 20 30 40 50 60

Temperature in °C

Vapour pressure in bar

R290

R134a

R404A

R22

R600a

4 CN.60.F1.02 November 2000

R 290 has roughly 90 % of R 22 or 150 % of R 134a volumetric capacity at 45 °C condens-

ing temperature, as seen in figure 2. Because of this the necessary compressor swept

volume is close to R 22 also, and 10 % to 20 % larger than for R 404A.

The volumetric capacity is approx. 2.5 to 3 times that of R 600a. Thus the choice for either

R 290 or R 600a will lead to differences in system design because of very different neces-

sary volume flow for same refrigeration need.

The volumetric cooling capacity is a value calculated from suction gas density and en-

thalpy difference of evaporation.

Figure 2: Volumetric capacity of R 290, R 134a, R 404A and R 600a, relative to R 22, over

evaporation temperature, at 45 °C condensing and 32 °C suction gas temperature, no

subcooling

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

1,1

-40 -30 -20 -10 0

Evaporation temperature in °C

Volumetric capacity rel. to R22

R290

R134a

R404A

R22

R600a

1.2 Capacity

November 2000 CN.60.F1.02 5

If R 290 would be charged into an unchanged refrigeration system, charge amount counted

in grams would be much lower. However, calculated in cm³, the charge would be roughly

the same liquid volume in the system. This gives charges of approx. 40 % of R 22 or R

404A charge in grams, according to the data from table 1, which also corresponds with

empirical values.

Maximum charge according to safety regulations is 150 g for household refrigerators and

similar applications, which corresponds to approx. 360 g of R 22 or R 404A.

Refrigerant R 290 specification is not found in international standards. Some data are

enclosed in the German standard DIN 8960 of 1998, which is an extended version of ISO

916. The purity of the refrigerant has to be judged from chemical and stability side, for

compressor and system lifetime, and from thermodynamic side regarding refrigeration

system behaviour and controllability.

The specification in DIN 8960 is a safe general hydrocarbons refrigerant specification,

adopted from other refrigerants criteria catalogue and covering propane, isobutane, normal

butane, and others. Some points can possibly be accepted a little less narrow for specific

refrigerants and impurities combinations after extensive evaluation.

For the time being no refrigerant quality according to an official standard is on the market.

The specifications of possible qualities have to be checked with the supplier in details.

Liquified petrol gas LPG for fuel applications or technical grade 95 % purity is not sufficient

for hermetic refrigeration. Water, sulfur and reactive compounds contents has to be on a

lower level than guaranteed for those products. Technical grade 99.5 %, also called 2.5, is

widely used.

Table 2: Specification of R 290 according to DIN 8960 - 1998

1) This content is not explicitly stated in DIN 8960. Only the impurities are listed and

limited. The main content is the rest up to 100 %.

2) From compressor point of view a butane content up to approx. 1 % is acceptable

in the R 290.

3) This is a maximum value for every single substance of the multiple unsaturated

hydrocarbons.

4) This is a maximum value for every single aromatic compound.

5) This is a preliminary value, to be reviewed with growing experience.

noitacificepStinU

tnetnoctnaregirfeR

≥≥

≥

≥≥

5.99ssamyb%

seitirupmicinagrO

≤≤

≤

≤≤

5.0ssamyb%

eneidatuB-3,1

≤≤

≤

≤≤

5ssamybmpp

enaxeHlamroN

≤≤

≤

≤≤

05ssamybmpp

enezneB

≤≤

≤

≤≤

1ecnatsbusrepmpp

rufluS

≤≤

≤

≤≤

2ssamybmpp

.pavefoedilgerutarepmeT

≤≤

≤

≤≤

5.0).llitsed%79ot5ta(K

sesagelbasnednocnoN

≤≤

≤

≤≤

5.1esahpruopavfo.lov%

retaW

≤≤

≤

≤≤

52ssamybmpp

tnetnocdicA

≤≤

≤

≤≤

20.0noitazilartueNg/HOKgm

eudisernoitaropavE

≤≤

≤

≤≤

05ssamybmpp

sdilos/selcitraPonkcehclausiV

1.3 Refrigerant charge

1.4 Purity

6 CN.60.F1.02 November 2000

Refrigerant R 290 is used with polyolester oil in Danfoss compressors, so material com-

patibility is almost identical to R 134a or R 404A situation from oil side. R 290 is chemically

inactive in refrigeration circuits, so no specific problems should occur there. Solubility with

ester oil is good. Direct material compatibility is less problematic. On some rubbers, plas-

tics and especially chlorinated plastics however, problems have been observed, but these

materials are normally not present in small hermetic systems. Some materials, on which

problems have been reported by different testers, are listed in the table 3. On critical

materials test have to be performed for the specified use.

Table 3: Material compatibility

For domestic refrigerators the common desiccant is a molecular sieve, a zeolithe. For R

290 a material with 3 Å pores is recommended, like for R 134a, e.g. UOP XH 7, XH 9 or XH

11, Grace 594, CECA Siliporite H3R. Pencil driers for R 134a can possibly be used for R

290, if they are tested according to IEC / EN 60 335 burst pressure demands.

See also note CN.86.A .

If hardcore driers are to be used, please ask the manufacturer for compatibility to R 290.

Danfoss type DU driers can be used.

lairetaMelbitapmoc

rebburcilytuBon

rebburlarutaNon

enelyhteyloPsnoitidnocnosdneped

PPon

CVPon

FDVPon

MDPEon

MSCon

2 Materials

2.1 Driers

November 2000 CN.60.F1.02 7

The main disadvantage discussed in connection with R 290 use is the risk based in its

flammability. This leads to necessity for very careful handling and safety precautions.

Table 4: Flammability of propane

Because of the flammability of propane in a wide concentration range safety precautions

are necessary, on the appliance itself and in the manufacturing factory. The risk assess-

ments behind these two situations are quite different. Main common starting point is, that

accidents need to have two essential preconditions. One is the flammable mixture of gas

and air and the other is the ignition source of a certain energy level or temperature.

These two have to be present together for combustions, so avoidance of this combination

has to be proven.

Figure 3: Yellow warning label

For safety testing of household refrigerators and similar applications a standard has been

established in Europe, IEC Technical Sheet TS 95006. It is also transferred to an amend-

ment to IEC / EN 60 335-2-24, which is the normal electrical safety standard. Approvals of

refrigerators using hydrocarbons as refrigerant are done according to the proceedures of

the TS in Europe since 1994. The methodology of TS and the amendments derived from

this are base for the following short description. Other applications have to take different

national standards and legislation into account, e.g. EN 378, DIN 7003, BS 4344, SN 253

130, which can have different demands.

• All electrical elements switching during normal operation are taken to be possible igni

tion sources. This includes thermostat, door contacts for lighting, on/off and other

switches, like superfrost, compressor relays, external klixon, defrost timers and so on.

• All refrigerant containing parts are taken to be possible refrigerant sources through

leaks. This includes evaporators, condensers, door heaters, tubings and the compressor

• Maximum refrigerant charge is set to be 150 g. By keeping the charge to max. 25 % of

lower explosion level LEL, which is approx. 8 g/m

, for a standard kitchen, ignition

risk is very low, even if refrigerant distribution in case of leakage is uneven for some

time first

The main target of the safety precautions is to seperate rooms with refrigerant containing

parts from rooms with switching elements.

Danfoss Compressors for R 290 have in-ternal

protectors and PTC starters or special relays,

both preventing from sparks coming out near

the compressor, because it can not be guar-

anteed to hold surrounding air below LEL in

case of leaks close to the compressor.

They are equipped with a yellow label warn-

ing for flammable gas, like shown in figure 3.

8122-4

R290

3.1 Appliance

)LEL(timilnoisolpxerewoL%1.2³m/g93.xorppa

)LEU(timilnoisolpxereppU%5.9³m/g771.xorppa

erutarepmetnoitingimuminiMC°074

3 Flammability and

Safety

8 CN.60.F1.02 November 2000

Figure 4: Appliance design variants

In figure 4 three principal possibilities are shown. Option 1 has evaporator and thermostat/

door switch both located in the storage volume. This is critical for flammable refrigerants

and should not be used. Option 2 has evaporator inside and thermostat/door switch out-

side, on top. This normally gives a safe solution. Option 3 has thermostat/door switch

inside, but evaporator foamed in place behind the inner liner. This is a possible solution

used in many cases. Choosen option has to be designed and proven in leakage test accord-

ing to TS 95006 and IEC / EN 60335 demands.

On many refrigerator or freezer designs this separation is already the existing situation.

• Large free standing bottle coolers and freezers often have all electrical switches in the

top panel.

• Some refrigerators have the evaporators hidden behind the liner, in the foam, means not

in the cabinet space where thermostats and so on are allowed in this case.

Critical situation is given whenever it is not possible to avoid evaporator and thermostat or

switches being in the cabinet. In this case two possibilities are left.

• Thermostats and switches have to be changed to sealed versions preventing gas from

penetrating them and thus reaching the switching contacts. Danfoss offers electronic

thermostats suitable for this application.

• Fans inside the refrigerated compartment have to be safe and sparkfree even if blocked.

• Electrical connectors and lamp holders have to be proven according to certain specifi-

ations.

Every R 290 appliance type has to be tested and approved according to the TS / IEC / EN

proceedures, by an independent institute, even if all above mentioned criteria are included

in the design. Please see the standards for details. Instructions for use should contain

some informations and warnings for careful handling, like not to defrost freezer compart-

ments with knives, and for installing in a room with at least 1 m³ of space per 8 g of charge,

the latter to be seen on the type label.

Systems using relays or other electrical components near the compressor must meet the

specifications. These are including

• Fans at the condenser or compressor must be sparkfree even when blocked or over

loaded. Either they have to be designed not to need a thermal switch, or this switch has

to meet IEC 60079-15.

• Relays have to meet IEC 60079-15 or being placed where a leakage can not produce a

flammable mixture with air, e.g. in a sealed box or at high altitude. The starting acces

sory of Danfoss SC compressors is delivered with a long cable for placing in a separate

electrical installation box.

1 32

Thermostat /

door switch

Evaporator

November 2000 CN.60.F1.02 9

The refrigerant containing system and the safety system design is to be approved and

controlled regularly by local authorities normally. Below the design principles for installa-

tions in Germany are given. In many details this is based on regulations for liquified gas

installations. Specialities are found around the charging stations, where gas connectors

are to be handled frequently and a charging of the appliances occurs.

The basic principles for safety are

• Forced ventilation to avoid local accumulation of gas.

• Standard electrical equipment except for the ventilation fans and safety systems.

• Gas sensors continuously monitoring in possible leakage areas like around charging

stations, with alarm and doubling of ventilation at 15 % to 20 % of LEL and with discon-

nection of all non explosion proof electrics in the monitored area at 30 % to 35 % of

LEL, leaving the fans running at full speed.

• Leakage test on appliances before charging to avoid charging of leaking systems.

• Charging stations designed for flammable refrigerants and connected to the safety sys-

tems.

Safety system design can be supported by suppliers of charging stations and gas sensing

equipment in many cases.

For handling of R 290 in small containers, the rules are less strict in some countries.

In many cases of transition from non flammable refrigerants to R 290 the appliance cabinet

has to be modified for safety reasons as listed in section 3.1. But changes can additionally

be necessary for other reasons.

Refrigerant containing system parts have according to IEC / EN 60335 to withstand a

specified pressure without leaking. High pressure side has to withstand saturation over-

pressure of 70 °C times 3.5, low pressure side has to withstand saturation overpressure of

20 °C times 5. This gives the following for R 290:

• 87 bar overpressure High Pressure side

• 36.8 bar overpressure Low Pressure side

National standards could have different specifications, depending on the application.

The refrigeration system efficiency will normally not cause a need for changing evaporator

or condenser size, means outer surface can be left the same as with R 22 or R 404A.

Inside design of the evaporator possibly needs some modification, because the refrigerant

volume flow is different, according to the compressor swept volume. To keep the refriger-

ant flow speed within the recommended range of 3 to 5 m/s it may be necessary to adopt

the cross flow sections.

Rollbond evaporators can maybe not be used because of the high demands on burst

pressure.

Special care has to be taken when designing the accumulator in the system. When using

R 22 or R 134a the refrigerant is heavier than the oil used, while with R 290 the refrigerant

is less heavy, as can be seen in the data table 1. This can lead to oil accumulation if the

accumulator is too large, especially too high, and has a flow path which does not guaran-

tee emptying sufficiently during startup phase of the system. Evaporator design hints can

be found in note CN.82.A .

4 Refrigeration

system design

4.1 Heat exchangers

3.2 Factory

10 CN.60.F1.02 November 2000

For R 290 experience shows the need for a capillary flow rate almost similar to R 404A. At

least this is a good starting point for optimization.

As with R 134a, R 404A and R 600a the suction line heat exchanger is very important for

system energy efficiency of R 290, which it was not for R 22, see figure 5. The figure

shows increase of COP with superheat from few K up to +32 °C return gas temperature,

where a range from +20 °C to approx. +32 °C is usual for small hermetic systems. This

large increase in COP for R 290 is caused by a high vapour heat capacity. In combination

with the need for keeping the refrigerant charge close to maximum possible in the system,

thus giving no superheat at evaporator outlet, the suction line heat exchanger has to be

very efficient for preventing air humidity condensation on the suction tube. In many cases

an elongation of the suction line and capillary gives efficiency improvements. The capillary

itself has to be in good heat exchanging contact with the suction line for as long a part of

total length as possible.

Figure 5: Theoretical COP increase of different refrigerants versus suction temperature

with adiabatic compression, internal heat exchange, at -25 °C evaporation, 45 °C conden-

sation, no subcooling before internal heat exchanger

At high superheat, with good internal heat exchange, the theoretical COP of R 290, R 600a

and R 134a is higher than for R 22. At very low superheat the COP of R 290, R 600a and R

134a is lower than for R 22. The R 290 behaviour is similar to R 134a, with respect to

internal heat exchange.

2,0

2,2

2,4

2,6

2,8

3,0

-25 0 25

Suction gas temperature in °C

Isentropic COP

R290

R134a

R404A

R22

R600a

4.2 Capillary

November 2000 CN.60.F1.02 11

Generally the same rules for evacuation and processing are valid as for R 22, R 134a or

R 404A systems. The maximum allowable content of non condensable gases is 1 %.

Too high level of non condensables increases energy consumption because of higher

condensing temperature and a portion of the transported gas being inactive. It can addi-

tionally increase flow noise.

The specifications for cleanliness are generally comparable to R 22 or R 134a. The only

official standard on cleanliness of components for refrigeration use is the DIN 8964, which

also is used in several countries outside Germany. It specifies maximum contents of

soluble, insoluble and other residues. The methods for determining soluble and insoluble

contents are to be modified for the actual refrigerant R 290, but in principle the same limits

are useful.

Servicing and repair of R 290 systems is possible for skilled and well trained service

technicians. Please see note CN.73.C for details. Local laws and regulations have to be

taken into account also. It needs very careful handling because of the flammability of the

gas, which is a potential danger during work on the refrigeration system. A good ventilation

of the room is necessary and the discharge of the vacuum pump has to be lead to open air.

The equipment of the service technician has to meet the requirements of R 290 in terms of

evacuation quality and refrigerant charge accuracy. An electronic scales is recommended

to control refrigerant charge to within the needed accuracy.

Conversion of a R 22, R 502 or R 134a system to R 290 is not recommended by Danfoss,

because these systems are not approved for flammable refrigerant use, so electrical safety

is not proven to be according to the needed standards.

TS 95006

Refrigerators, food-freezers and ice-makers using

flammable refrigerants

, Safety Requirements,

Ammendment to IEC 60 335-2-24, CENELEC, July 1995

CN.86.A

Driers and Molecular Sieves Desiccants

CN.82.A

Evaporators for Refrigerators

CN.73.C

Service on Household Refrigerators and Freezers

with New Refrigerants

CN.60.E

Practical Application of Refrigerant R 600a Isobutane

in Domestic Refrigerator Systems

EN 60335-2-24

Safety of household and similar appliances Part 2:

Particular requirements for refrigerators,

food freezers and ice-makers

4.3 Evacuation

4.4 Cleanliness

of components

5 Service

References

Danfoss can accept no responsibility for possible errors in catalogues, brochures and other printed material. Danfoss reserves the right to alter its products without notice. This also applies to

products already on order provided that such alterations can be made without subsequential changes being necessary in specifications already agreed.

CN.60.F1.02 Produced by Danfoss November 2000

The Danfoss product programme

for the refrigeration industry contains:

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Compressors for Refrigeration and Air Conditioning

A wide range of hermetic reciprocating compressors and scroll compressors

as well as aircooled condensing units. The product range is applied in air

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Appliance Controls

For the regulation of refrigeration appliances and freezers Danfoss supply a

CFC-free product range of electromechanical thermostats for refrigerators and

electromechanical thermostats for refrigerators and freezers produced according

to customer specification; Hermetic valves for refrigerator/freezer combina-

tions and for energy saving applications; Service thermostats – for all refrigerat-

ing and freezing appliances.

Refrigeration and Air Conditioning Controls

With our full product range we cover all the requirements for mechanical and

electronically controlled refrigeration systems. The functions cover: control, safety,

system protection and monitoring. Our products are applied for all commer-

cial- and industrial refrigeration applications as well as for air conditioning.

Compressors for Refrigerators and Freezers

Hermetic compressors and fan-cooled condensing units for household refrig-

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tions such as sales counters and bottle coolers. Compressors for heating

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commercial vehicles, buses, and boats.

Danfoss Refrigerant R290 Propane in Small Hermetic Systems Installation guide

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